Technical Field
The present disclosure relates to a motor controller.
Related Art
Semiconductors such as Field Effect Transistors (FETs), acting as switching elements, are mounted to inverter circuits that perform drive control of a motor. There is a risk of damage when the semiconductors such as FETs reach a specific temperature, or above.
In general, a thermistor, with a resistance value that varies according to temperature variation of a circuit board, is mounted on the circuit board to which the inverter circuit is mounted, and the temperature of the circuit board is detected from variations in the resistance value of the thermistor. In cases in which the temperature based on the detection result of the thermistor has reached a specific threshold value or above, a duty ratio of voltage applied to the motor is reduced, and the temperature increase of the switching elements is suppressed.
However, depending on the design of the circuit, the thermistor cannot necessarily be mounted in the vicinity of the switching elements of the inverter circuit. In cases in which the thermistor is mounted at a location a distance away from the switching elements, a correlation relationship between the temperature of the circuit board computed from the detection result of the thermistor, and the temperature of the switching elements needs to be derived. Further, the temperature threshold value, this being a determination criterion for lowering the load on the switching elements, is set low, such that the switching elements can be reliably protected.
However, there has been an issue in that, when reliability of protection of the switching elements is prioritized, the temperature threshold value is set low, such that the voltage applied to the motor is reduced more frequently, and it is difficult to stably rotate the motor at high output.
Japanese Patent Application Laid-Open (JP-A) No. 2009-278802 describes an techniques of a motor drive circuit in which the temperature of switching elements is detected based on a detected current value and a detected voltage value.